The present invention relates to an emulsion composition comprising a fluorocarbon silane or hydrolyzate thereof and coated composition produced therefrom.
Some silane-containing aqueous solutions that can provide water-repellent characteristics on the surface of a substrate have been disclosed. See, e.g., U.S. Pat. Nos. 4,648,904, 4,757,106, 4,990,377, 5,196,054, 5,550,184, and 5,664,014, European Patent 0 748 357, and Japanese Kokai Patent Application No. Hei 11(1999)-181355.
For example, U.S. Pat. No. 5,550,184 discloses reactive hydrolyzed silane emulsions produced by emulsifying a hydrolyzable alkoxysilane in water in the presence of a high HLB value emulsifier to simultaneously retain the hydrolyzable alkoxysilane in substantially totally hydrolyzable state. The emulsion can produce durable coatings that impact water-repellent characteristics on a substrate.
Japanese Kokai Patent Application No. Hei 11(1999)-181355 discloses an emulsion containing a specific type of silane hydrolyzate, a specific type of silicate a substance, and a surfactant. The emulsion, however, requires pH adjustments to alkaline region in order to exhibit water-repellency and heat resistance characteristics.
Therefore, it is desirable to develop a new emulsion or coating containing the emulsion that does not require the alkaline pH adjustment to exhibit the desired heat-resistance and water-repellency properties.
Additionally, though these emulsions exhibit water-repellency characteristics, they do not exhibit oil-repellent property. For example, glass window of oven, range, or toaster can be coated with a layer formed by an emulsion having good water repellency at high temperature, but it has a poor oil-stain resistance. Therefore, it is also highly desirable to develop an emulsion that can exhibit both water-repellent and oil-repellent properties for a variety of applications.
Therefore, it is desirable to develop a new emulsion or coating containing the emulsion that does not require the alkaline pH adjustment, or without the need of metal hydroxide or the chemicals disclosed above, to exhibit the desired heat-resistance and water-repellency properties.
Additionally, though these emulsions exhibit water-repellency characteristics, they do not exhibit oil-repellent property. For example, glass window of oven, range, or toaster can be coated with a layer formed by an emulsion having good water repellency at high temperature, but it has a poor oil-stain resistance. Therefore, it is also highly desirable to develop an emulsion that can exhibit both water-repellent and oil-repellent properties for a variety of applications.
A composition comprises a fluorocarbon silane or hydrolyzate thereof; a surfactant; a polymerizable, silicon-containing compound; and a catalyst.
The fluorocarbon silane generally contains at least one hydrolyzable fluorocarbon silane and can be represented by Rfxe2x80x94(CH2)pxe2x80x94Si{xe2x80x94(Oxe2x80x94CH2CH2)nxe2x80x94ORxe2x80x2}3 where Rf can be one or more C3-18 perfluoroalkyl groups, each Rxe2x80x2 can be the same or different and is independently a C1-3 alkyl groups or combinations thereof, p=2-4, and n=2-10). The preferred Rf is mixed perfluoroalkyl groups of 8 to 18 carbons.
Examples of the fluorocarbon silanes include, but are not limited to, perfluoroalkylethyltris (2-(2-methoxyethoxy)ethoxy)silane when n is 2, and perfluoroalkylethyltris (2-(2-(2-methoxyethoxy)ethoxy)ethoxy)silane when n is 3, and combinations thereof. These fluorocarbon silanes are either commercially available or can be produced by any means known to one skilled in the art as disclosed in Kir-Othmer Encyclopedia of Chemical Technology, 3rd edition, vol. 20. For example, the fluorocarbon can be produced by the method disclosed in U.S. Pat. No. 5,550,184, disclosure of which is incorporated herein by reference.
Any surfactant that can emulsify the hydrolysis product of the fluorocarbon silane can be used. The surfactant generally is a surfactant having an HLB value sufficiently high to inhibit self-condensation of the fluorocarbon silane hydrolysis product. The term xe2x80x9cHLBxe2x80x9d refers to the HLB system published by ICI America""s, Inc., Wilmington, Del.; Adamson, A. W., xe2x80x9cPhysical Chemistry of Surfacesxe2x80x9d, 4th edition, John Wily and Sons, New York, 1982). The surfactant can be anionic, cationic, nonionic, amphoteric, or combinations thereof. The preferred surfactants are those with HLB values greater than 12, more preferably greater than 16. Generally, the lower HLB value the surfactant is, the larger amount of the surfactant is required to stabilize the emulsion. Two or more miscible surfactants generally can also be combined or mixed for use as long as they are surfactants having HLB values sufficiently high to inhibit self-condensation of the fluorocarbon silane hydrolysis products.
The HLB value of a nonionic surfactant can be determined by calculation with a formula, among others, originated by Griffin of Atlas Co. (now ICI America) in the U.S. However, in the case of the anionic type or the cationic type, a method for determination by calculation of the HLB value is not available to date. Nevertheless, paying attention to the fact that changes in emulsification characteristics are sensitive to changes in the HLB value, Atlas Company established and published a method for the experimental determination of the HLB value by an emulsification experiment on standard oil. Companies other than Atlas have also established methods for experimental determination of HLB value. However, it can be clarified by the adoption of any experimental method that the HLB value of the anionic type or the cationic type is greater than 16.
Examples of nonionic surfactants include, but are not limited to, Rxe2x80x2fxe2x80x94CH2CH2xe2x80x94Oxe2x80x94(CH2CH2O)11xe2x80x94H, C9H19xe2x80x94C6H4xe2x80x94Oxe2x80x94(CH2CH2O)50xe2x80x94H, other nonionic surfactants, and combinations thereof Examples of cationic surfactants include, but are not limited to Rxe2x80x2fxe2x80x94CH2CH2SCH2CH(OH)CH2N(CH3)3+Clxe2x88x92, other cationic surfactants, and combinations thereof. Examples of anionic surfactants include, but are not limited to, C12H25(OCH2CH2)4OSO3xe2x88x92NH4+, C12H27xe2x80x94C6H4xe2x80x94SO3xe2x88x92Na+, other anionic surfactants, and combinations thereof. In each of the formulae, Rfxe2x80x2 is a perfluoroalkyl group generally having about 3-18 carbon atoms. The preferred surfactants are nonionic surfactants having polyethylene glycol in the molecular chain.
The content of the fluorocarbon silane in the water-based emulsion can be about 0.1 weight % or higher, preferably about 2-20 weight %, and most preferably 7-15 weight %, based on the total weight of the emulsion. The weight ratio of the fluorocarbon silane to the surfactant can be in the range of from about 1:1 to about 10:1, preferably about 10:2 to about 10:5, and even more preferably 10:3.
Any polymerizable, silicon-containing compound can be used so long as it can copolymerize with the fluorocarbon silane hydrolysis product to improve heat-resistant water-repellent characteristics, heat-resistant oil-repellent characteristics, or both. Suitable polymerizable, silicon-containing compounds include silicates, organosilanes, or combinations thereof.
A suitable silicate can have the formula of Sixe2x80x94R4 where R is one or more groups selected from the group consisting of OCH3, OCH2CH3, (OCH2CH2)mOCH3, and combinations thereof in which m=1-10, preferably 1-3. Because a silicate represented by Sixe2x80x94((OCH2CH2)mOCH3)4 (m=1-3) is water-soluble, it can dissolve in a water-based emulsion containing a fluorocarbon silane hydrolysis product in a relatively short time, the silicate represented by Sixe2x80x94((OCH2CH2)2OCH3)4 is presently preferred.
The silicate to the fluorocarbon silane molar ratio can be in the range of from about 0.3:1 to about 10:1, preferably 0.3:1 to 5:1, and most preferably 0.4:1 to 2:1 Suitable organosilane include organoalkoxysilanes having the formula of R2qSi(OR3)4-q where each R2 can be independently an alkyl group having 1 to about 10 carbon number; each R3 can be the same or different and each is independently an alkyl group having 1 to about 3 carbon number; and q=1-3. Examples of suitable organosilanes include, but are not limited to, methoxysilanes, ethoxysilanes, propoxysilanes, and combinations thereof.
The molar ratio of organoalkoxysilane to fluorocarbon silane can be in the range of from about 0.3:1 to about 10:1, preferably 0.3:1 to 5:1, and most preferably 0.4:1 to 2:1.
The catalyst can be either an acid or a pH-adjusting agent. An aqueous acid such as phosphoric acid, boric acid, hydrochloric acid, sulfuric acid, nitric acid, acetic acid, oxalic acid, or combinations thereof can be used as acid for the composition.
The presently preferred catalyst, if a silicate is used as silicon-containing compound, is phosphoric acid, boric acid, or combinations thereof.
If an organosilane is used as the silicon-containing compound, the aqueous solution of the above-disclosed acid or aqueous alkaline solution such as ammonia, pyridine, sodium hydroxide, or potassium hydroxide, can be used as catalyst. Aqueous phosphoric acid solution is especially suitable.
The amount of catalyst is generally an effective amount that can produce an emulsion having the characteristics disclosed. It is also an amount, when a silicate is used, that can adjust the pH of the emulsion to 4.5 or less, preferably less than 2.2 such as about 2.0 depending on the catalyst. If an organosilane is used, there is no pH limitation. However, if a higher pH is desired, an aqueous alkali solution can be used to adjust the pH to 7.0 or more, especially 7.0-12.
The heat-resistant water-repellent characteristics of the coated layer produced from the emulsion composition can be effectively improved by either adjusting its pH to alkaline region or, if a silicate is used as the silicon-containing compound, acidifying to acidic region using, for example, phosphoric acid, boric acid, or combinations thereof.
The emulsion composition of the present invention can contain a pigment, a bactericide, an ultraviolet ray absorbent, an antioxidant, or other customarily used additives in a range without affecting the stability of the emulsion and the heat-resistant water-repellent characteristics of the coated layer.
Any methods known to one skilled in the art can be used for the preparation of the emulsion composition of the present invention. The components can be combined in any order to produce the composition.
However, it is preferable to dissolve a surfactant in water followed by addition of a fluorocarbon silane slowly, such that self-condensation of the fluorocarbon silane is inhibited and a hydrolyzed state of the fluorocarbon silane is maintained, with agitation such as stirring, any additives desired, the catalyst, and finally the polymerizable, silicon-containing compound. Generally the pH is not appreciably affected by the addition of the silicon-containing compound. This process can be best used to inhibit self-condensation and to maintain a hydrolyzed state of the fluorocarbon silane.
The water-based emulsion of the present invention can be coated with or to any substrate. The substrates are rendered water-repellent, oil-repellent, or both characteristics by coating the emulsion on the substrate surface followed by drying. Examples of suitable substrates include, but are limited to, aluminum, stainless steel, or other metal sheets, glass, glass sheet, ceramic tile, brick, concrete, stone, wood, masonry, fiber, leather, plastics, or other substrate that can be used under high temperature conditions. The coating of the water-based emulsion on a substrate can be carried out by any methods known to one skilled in the art such as, for example, dipping method, spray method, spin coating method, roll coating method, or other publicly known methods. The dipping method is preferred because it does not cause damage to transparency on a glass substrate.
Heating can also be carried out in order to accelerate the drying process. In general, drying is carried out in a temperature range of about 100-350xc2x0 C. for about 5 minutes to 24 hours.
Furthermore, before coating the water-based emulsion of the present invention on a substrate, a silicone compound such as, for example, silica, can be coated to form a base or backing layer. By coating the emulsion on top of this layer, the heat-resistant water-repellent characteristics can be maintained for an prolonged period. The substrate after the coating with the emulsion composition, if necessary, can be washed with water after it is dried to remove the residual surfactant.